1. Field of the Invention
The present invention relates to a steering system for an automotive vehicle having two pairs of dirigible road wheels, and more particularly to a rear wheel steering mechanism adapted for use in a four-wheel steering system capable of steering the dirigible rear road wheels in response to steering operation of the dirigible front road wheels.
2. Description of the Prior Art
In such a four-wheel steering system as described above, there is provided a linkage such as a rotary shaft or a reciprocable link arranged in a fore-and-aft direction of the vehicle and drivingly connected at its front end to a front wheel steering mechanism to be moved in response to steering operation thereof, and a connecting mechanism arranged to drivingly connect the linkage to an operation rod of a rear wheel steering mechanism in such a manner that the operation rod is displaced in an axial direction in response to movement of the linkage to steer the dirigible rear road wheels. In Japanese Patent Early Publications Nos. 59-26363, 59-26364 and 59-26365, there has been proposed such a connecting mechanism adapted for use in combination with the rear wheel steering mechanism, wherein the connecting mechanism is designed to vary the ratio of the steering angle of the rear road wheels relative to that of the front road wheels and to vary the steering direction of the rear road wheels relative to that of the front road wheels. The connecting mechanism includes an input shaft in drive connection to the linkage for rotation therewith, an output shaft swingably connected at its one end to the input shaft by means of a universal joint and being integrally connected at its other end with an operation rod of the rear wheel steering mechanism, and drive means arranged to incline the output shaft with respect to the input shaft. In operation of the connecting mechanism, an inclined angle of the output shaft with respect to the input shaft is controlled by activation of the drive means to vary the steering angle ratio and direction of the rear road wheels. In such control of the output shaft, however, the operation rod of the rear wheel steering mechanism is inevitably displaced in an axial direction even when the input shaft is being stationary. This causes change in the alignment, particularly toe-in, of the rear road wheels, resulting in deterioration of the steering stability of the vehicle.